It is known to provide trailers for motor vehicles and the like consisting of a casing mounted on two wheels disposed side by side and having a central towing bar, the front end of which is hitched to the rear end of the two-wheeled vehicle. These rearwardly-located trailers have a general tendency to render a ride with a motorcycle much more dangerous: for instance, during emergency braking, the tow-bar exerts a push on the vehicle which can cause a dangerous jack-knife effect. Such known trailers have also a limited load-carrying capacity.